The proposed study will investigate the noradrenergic system and its influence on the action of testosterone in relation to vocal behavior in a songbird species the European starling (Sturnus vulgaris). First, sources of noradrenergic input to telencephalic areas of the starling vocal control system will be determined through use of tract- tracing techniques in combination with immunocytochemical markers of catecholaminergic activity (dopamine beta hydroxylase [DBH] and tyrosine hydroxylase [TH]). Identified sources of noradrenergic innervation will then be damaged with electrolytic lesions and the consequences of disrupting this input on monoamines levels in the telencephalic song nuclei will be assessed by high performance liquid chromatography (HPLC). The second portion of this study will address the role of afferent input from norepinephrine (NE) in maintaining hormone-induced plasticity in adulthood. This will be addressed in two experimental contexts; 1) photoperiod-induced seasonal changes in volume of the hyperstriatum ventrale pars caudale (HVC) of male and female starlings, 2) the production of "male-like" song in female starlings and accompanying volume changes in HVC after T implants. By evaluating the effects of testosterone manipulations on adult song behavior and HVC volume after the use of electrolytic lesions to remove sources of noradrenergic input to song nuclei, new insights into the role of the noradrenergic system in maintaining testosterone-dependent neural and behavioral responses can be gained.